I'm planning to use the think-aloud protocol for an upcoming usability test. A book chapter on think-aloud suggested that you show the participant an example video of someone thinking aloud. I think this is a good idea to reassure users that they are 'doing it' correctly as to get the best information from them.
That said, do any of you know of a good video to use for this? I'm thinking of using a video from a past test, but wanted to avoid that if possible.
I don't recommend that you show the participant a video of how to think-aloud, since they might try to mimic the kind of remarks the person in the video is saying. Just explain clearly to the participant what he's supposed to do, and whenever you see him spending a few seconds on a page and/or seem to be thinking, just ask him "what's on your mind?". This will get him to "get it" and think aloud more.
I've never used a video either. We usually have the participant try it out on a simple example before getting into the actual test. That lets them get acquainted with the technique and gives the experimenter a chance to correct the technique, if necessary.